The present invention generally relates to the field of pyrotechnic initiators, and more particularly to a pyrotechnic initiator having a slip plane between an ignition charge and an output charge.
Pyrotechnic initiators have many uses in industrial and consumer applications. One important use is in triggering the inflation of airbags in motor vehicles. Significant efforts have been made in the automotive industry to reduce the cost of manufacturing reliable airbag initiators. One advance has been the use of liquids and slurries in loading pyrotechnic charges into the initiators. As shown in U.S. Pat. No. 5,686,691 to Hamilton et al., it is known to load a slurry charge into a conventionally cup-shaped charge can, and to directly affix such a loaded can onto a header assembly so that the charge comes into contact with the header surface and bridgewire. However, this method poses certain drawbacks and difficulties in the loading and proper retention of the charge on the bridgewire.
For example, a monolithic dried slurry charge extending from the header assembly's top surface substantially up to the upper interior surface of the can is prone to moving out of optimal contact with the bridgewire when exposed to environmental and/or physical stresses. The higher the monolithic charge is, the longer the length of the surrounding container (such as a charge can) that is available to receive physical and environmental forces that can be transmitted through the upper region of the monolithic charge and into the lower region of the monolithic charge, where the charge makes contact with the bridgewire. Thus, the height of the monolithic charge increases the forces that are subjected upon the lower region of the charge including its portion contacting the bridgewire. Such increased forces can include direct lateral forces on the charge, which tend to shear the charge away from its position of intimate contact (which is generally provided or at least enhanced through the contraction and/or sealing of the charge around the bridgewire that occurs upon drying of the slurry) with the bridgewire. Such forces may also include torque that is transmitted by the enclosure acting as a lever arm with a pivot at or near its connection to the header assembly (e.g., a circumferential through-weld), thus tending to rip the lower region of the charge up from the top header surface and its attached bridgewire.
It is believed that these problems of such monolithic charges have not been addressed by employing a relatively low monolithic ignition charge that is separated from an overlying output charge by an intermediary slip plane.